Sure thing! We've got 669 and we're gonna multiply it by 31. That's the same as adding 669 to itself 31 times.
Step 1: 0 + 669 = 669
Step 2: 669 + 669 = 1338
Step 3: 1338 + 669 = 2007
Step 4: 2007 + 669 = 2676
Step 5: 2676 + 669 = 3345
Step 6: 3345 + 669 = 4014
Step 7: 4014 + 669 = 4683
Step 8: 4683 + 669 = 5352
Step 9: 5352 + 669 = 6021
Step 10: 6021 + 669 = 6690
Step 11: 6690 + 669 = 7359
Step 12: 7359 + 669 = 8028
Step 13: 8028 + 669 = 8697
Step 14: 8697 + 669 = 9366
Step 15: 9366 + 669 = 10035
Step 16: 10035 + 669 = 10704
Step 17: 10704 + 669 = 11373
Step 18: 11373 + 669 = 12042
Step 19: 12042 + 669 = 12711
Step 20: 12711 + 669 = 13380
Step 21: 13380 + 669 = 14049
Step 22: 14049 + 669 = 14718
Step 23: 14718 + 669 = 15387
Step 24: 15387 + 669 = 16056
Step 25: 16056 + 669 = 16725
Step 26: 16725 + 669 = 17394
Step 27: 17394 + 669 = 18063
Step 28: 18063 + 669 = 18732
Step 29: 18732 + 669 = 19401
Step 30: 19401 + 669 = 20070
Step 31: 20070 + 669 = 20739

So, 669*31 = 20739